1. Field of the Invention
The present invention relates to a so called helical scan type magnetic recording reproducing apparatus used for a video cassette recorder (VCR), digital audio tape recorder (DAT) or the like in which information is recorded/reproduced on a magnetic tape with a predetermined angle of inclination with respect to longitudinal direction of the tape. More specifically, the present invention relates to a magnetic recording reproducing apparatus in which loading and unloading of a magnetic tape are effected in a plane approximately parallel to a reference plane of a cassette, which is a plane formed by a center line of the magnetic tape when it is contained in a tape cassette.
2. Description of the Background Art
So called helical scan type tape travelling systems in which magnetic tape is travelled obliquely wound around a rotary drum can be classified into various loading methods, dependent on the angle of inclination of the drum, the direction of inclination, reference height, arrangement of tape guides and so on. A so called M loading method is a representative loading method in the helical scan type, which is employed in VHS, 8 mm VCR or in an R (Rotary)-DAT. A conventional tape driving system employing M loading method will be described with reference to FIGS. 8A and 8B.
In the conventional tape traveling system of M loading type, referring to FIG. 8A, a magnetic tape 2 going out from a supply reel 1a in a tape cassette 1 passes over a tension roller 12, an impedance roller (hereinafter referred to as "SI roller") 14 on the tape supply side, and a guide roller 16 on the supply side, and the tape traveling plane is inclined by an inclined guide 18 of the supply side. Thereafter, magnetic tape 2 travels wound helically on a rotary head drum 3 which is inclined in the direction shown by the arrow A of FIG. 8A, and magnetic signal is recorded/reproduced by rotary head drum 3. Magnetic tape 2 going away from rotary head drum 3 travels with its plane returned from the inclined state to the state allowing accommodation in the tape cassette by means of inclined guide 22 on the take up side, passes over guide roller 24 on the take up side, and travels at a constant speed between capstan 4 and pinch roller 5. Thereafter, magnetic tape 2 passes around guide 28 and wound around take up reel 1b.
The magnetic recording reproducing apparatus of the M loading method is advantageous in that the number of parts is small as the tape traveling system is relatively simple, and that the mechanism can be made thin, since loading of tape guides and the like is performed approximately parallel to the reference plane of the cassette. Details of such magnetic recording reproducing apparatus of the M loading method is disclosed in Japanese Patent Laying-Open No. 57-212651.
However, in the above described conventional magnetic recording reproducing apparatus of the M loading method, the height of lead 3a provided on the side of a fixed portion of rotary head drum 3 becomes higher than the lower end of a magnetic tape contained in tape cassette in the take up side region of the magnetic tape (on the side where magnetic tape goes away from the rotary head drum during traveling for recording/reproducing), as shown in FIG. 8B. Therefore, when the magnetic tape is to be loaded and unloaded approximately parallel to the reference plane of the cassette, the lower end of the magnetic tape may possibly be in contact with the edge of lead 3a, damaging the magnetic tape. Especially at the time of unloading the magnetic tape, magnetic tape 2 is pinched between lead 3a and a flange 24a of guide roller 24 on the take up side which regulates the height of the tape, and therefore the lower end of magnetic tape 2 may be damaged considerably.
Japanese Patent Laying-Open Nos. 57-191865 and 57-212649 disclose magnetic recording reproducing apparatus employing the above described M loading method in which rotary head drum 3 is slightly inclined to the side of the tape cassette so as to suppress increase in tape tension during traveling of the magnetic tape. In the magnetic recording reproducing apparatus disclosed in these laid-open applications, rotary head drum 3 is slightly inclined to the side of the tape cassette as compared with the above described conventional M loading method, whereby the tape winding angle around the inclined guide 18 on the supply side is made larger than the tape winding angle around the inclined guide 22 on the take up side, so that increase in tension of the magnetic tape 2 at the inclined guide 22 on the take up side, the tension value of which has been regulated on the supply side of rotary head drum 3, can be suppressed. As a result, load in winding the tape at capstan 4 can be reduced, and power consumption can be suppressed. As rotary head drum 3 is slightly inclined to the side of tape cassette 1 in this method, the position of lead 3a is also made slightly lower, as shown in FIG. 9B (or FIG.10B). However, even in this method, contact of the lower end of the magnetic tape 2 and the edge of lead 3a at loading and unloading of the magnetic tape is unavoidable, and therefore the tape edge is inevitably damaged. More specifically, the lead 3a is still not low enough, and in order to further lower the lead, it is necessary to increase the angle of inclination of rotary head drum 3 toward the side of tape cassette 1. However, if rotary head drum 3 is inclined to that extent, the winding angle of the magnetic tape around inclined guide 22 on the take up side cannot be ensured, and the tape traveling system cannot be implemented.
The problems of the above described conventional M loading method and of the magnetic recording reproducing apparatus disclosed in Japanese Patent Laying-Open No. 57-191865 and so on will be summarized, with reference to FIGS. 10A and 10B. Positional relation between lead 3a and the lower edge of the magnetic tape at the time of loading and unloading of the magnetic tape in the conventional M loading method shown in FIGS. 8A and 8B is illustrated in FIG. 10A. The line denoted by the arrow B of FIG. 10A indicates the position of the lower end of the magnetic tape accommodated in the tape cassette and the hatched region indicates the region of the magnetic tape which moves wound around rotary head drum 3 at the time of loading and unloading. As can be seen from this figure, at the time of loading and unloading of the magnetic tape, lead 3a is positioned above the lower end of the magnetic tape on the tape take up side region of rotary drum 3, so that the lower end of the magnetic tape and the edge of lead 3a cross and are in contact with each other. Therefore, the lower end of the magnetic tape is damaged by the edge of lead 3a.
The positional relation in the loading method disclosed, for example, in Japanese Patent Laying-Open No. 57-191865 which corresponds to FIG. 10A, is illustrated in FIG. 10B. As can be seen from this figure, in this method, lead 3a as a whole is lowered, as rotary head drum 3 is slightly inclined to the side of the tape cassette. However, contact between the lower end of the magnetic tape and the edge of lead 3a at the time of loading and unloading of the magnetic tape is still unavoidable.
Meanwhile, in order to avoid the damage at the lower end of the magnetic tape caused by the lead of the rotary head drum, Japanese Patent Laying-Open No. 4-205844, for example, proposes notching part or all of the lead, so that contact of the lower end of the magnetic tape with the edge of the lead at the time of loading and unloading of the magnetic tape is prevented. However, as it is desirable to guide the lower end of the traveling magnetic tape by providing a lead in the entire region of the rotary head drum where the magnetic tape is wound in order to ensure format compatibility or track linearity, it is not preferable to notch even a portion of the lead in order to avoid contact between the magnetic tape and the lead.
Especially, the magnetic tape becomes thinner and thinner recently and the lower end of the magnetic tape becomes more susceptible to damage. Therefore, solution of the above described conventional problem has been strongly desired.
Japanese Patent Laying Open No. 5-36169 discloses a prior art example of the helical scan type magnetic recording reproducing apparatus in which two inclined guides are included in the guide group on the take up side. In the magnetic recording reproducing apparatus disclosed in this article, referring to FIG. 11A, magnetic tape 2 going out from the tape cassette travels passing through inclined guide 118 on the supply side, first and second guide rollers on the supply side, and is helically wound around rotary head drum 103. Magnetic tape 2 moving away from rotary head drum 103 is first wound around first guide roller 124 on the take up side, passes through first inclined guide 122 on the take up side and passes guide roller 125, inclined guide 126 and extracting guide roller 127 on the take up side, travels at a constant speed pinched between capstan 104 and pinch roller 105, and returns to the tape cassette.
Though two inclined guides are provided on the tape take up side in this magnetic recording reproducing apparatus, these are provided merely to suppress tape tension by reducing winding angle of magnetic tape over the guides and the purpose of providing these two guides is not to avoid contact between the lead and the magnetic tape, which is the object of the present invention to be described later.
In the magnetic recording reproducing apparatus of this article, the second guide roller 117 on the supply side is arranged immediately before magnetic tape 2 is wound around rotary head drum 103, and the first guide roller 124 on the take up side is provided immediately after the tape moves away from rotary head drum 103 in order to attain the above described objects, which is different from that of the present invention. When a tape traveling system is implemented with the guide rollers arranged in this manner, as can be seen from FIG. 11B, there is a large gap between the position of the second guide roller 117 on the supply side and the first guide roller 124 on the take up side, and thus the resulting system is far from parallel loading to which the present invention is applied.
Therefore, as will become apparent after reading the rest of this disclosure, even those skilled in the art cannot readily attain the object of the present invention by simply combining the structure of the tape guides of the magnetic recording reproducing apparatus disclosed in the aforementioned laid-open patent application with the conventional magnetic recording reproducing apparatus employing M loading method.